System of selective signaling



June 23, 1931. GA. SOMERSALO SYSTEM OF SELECTIVE SIGNALING Filed Aug.15, 1927 2 Sheets-Sheet 1 IN V EN TOR.

June 23, 1931. G. A. SOMERSALO SYSTEM OF SELECTIVE SIGNALING Filed 'Aug.15, 1927 2 Sheets-Sheet 2 Q/N VEN TOR. d. v

" ATTORNEY Patented June 23, 1931 PATENT] OFFICE GEORGE A. SOMERSALO, OFNEW YORK, N. Y.

SYSTEM OI SELECTIVE SIGNALING Application filed August 15, 1927. SerialNo. 212,872.

My invention relates to an electric circuit for the selectivetranslation of oscillating currents of a desired frequency or band offrequencies.

In particular, my invention relates to a selective electric circuit inwhich a number of tuned circuits are connected in cascade by a specialform of coupling to reduce to a minimum the reaction of one tunedcircuit upon another. i

Heretofore, in systems for the selective transmission of waves, it wascommon practice to connect several tuned circuits in cascade by one ofseveral types of coupling in which there was always an appreciableamount of reaction between two adjacent circuits. The reaction betweenthe circuits destroys the selective property of the tuned circuits andflattens out the resonance curve,

and, in the limit, may produce a doublepeaked resonance curve. In priorarrangements, the coupling between circuits had to be made very loose inorder to prevent the reaction from destroying the selectivity.

But, loose coupling prevents the efficient transfer'of energy from onecircuit to another. In one known arrangement, in order to reduce thereaction, and at the same time obtain good energy transfer betweencircuits, it was proposed to couple adjacent cir'- cuits by vacuum tuberelays, thus taking advantage of the supposedly unilateral couplingeffect of the tube. But it is nowcommon knowledge thata vacuum tuberelay is not unilateral in its coupling effect, due to the inherentcapacity'effect between its various electrodes, but will produceundesired reac-. tions between the coupled circuits.

It is, therefore, an object of my invention 40 to devise a selectivecircuit in which full advantage is obtained of the selective property ofall the coupled circuits and, at the same time, elficient energytransfer is obtained without the use of vacuum tube relays. While myinvention is capable of use generally where it is desired to selectwaves of a particular frequency or band of frequencies to the exclusionof others, it is particu larly useful as a selective element in a radio59 receiving set.

I have illustrated certain features of my invention in the accompanyingdrawings, in which,

Fig. 1 is a diagram of a wavemeter calibrating' circuit employing thewell known unilateral type of connection to the detector, which type ofconnection is used in a new relation in my invention.

Fig. 2 is a vector diagram showing the relations between the variouselectric quantities in the circuit of my invention.

Fig. 3 is a diagram of a circuit embodying the principles of myinvention.

Fig. 4 is a circuit diagram of a modified forni of my invention.

Fig. 5 is a circuit diagram of still another form of my invention.

Fig. 6 is a circuit diagram showing the preferred form of my inventionas embodied in a commercial radio receiving set.

Fig. 6 is a slightly modified form of the preferred circuit.

Referring to Fig. 1, a well known arrangement for calibrating wavemetersis shown, and is reproduced here for the purpose of explaining theprinciple of operation of my invention. A standard wavemeter circuitincluding an inductance 1 and a variable condenser 2 is excited in aknown manner by a buzzer H, which is provided with a shunting condenserK and an operating battery B. The wavemeter to be calibrated comprises avariable condenser 4 and an inductance coil 3 inductively coupled tocoil 1. A telephone 6, shunted by a de- 85 tector 7, is connected by asingle wire 5 to one terminal of the wavemeter circuit 3, i. This isknown as a unilateral connection. When wavemeter 3, 4; is tuned to thecurrents generated by the standard wavemeter, 90 the buzzer note will beaudible in telephone 6, notwithstanding the fact that there is no returnconnection of either the phone or the detector to the circuit 3, 4:.This phenomena is known to those skilled in the art, and does 95 notrequire an explanation, but for the purpose of explaining my presentinvention I offer the following theory: When circuit 8,

4 is excited, there will be a variable current p ure in lead This urrentressure be forced partly through the telephone coil operation of Fig.1?)is as follows:

is similar to that in any conductor connected with an electric circuit.As the current pressure in a cable forces the electrons nearer thesurface, the electrons here will be forced to the end of the lead 5 andfrom here to the telephone coil. If the telephone coil were not shuntedby a detector 7,-notl1- ing wouldhappen. Now. the electronswill 6, andpartly against the detector 7. The reaction of these two against such apressure is different; The coil will act'like an elastic wall, theactionandthereaction being" equal and opposite. The first transient waveimpulse will magnetize the core and the magnetization will set up anopposing electromotive force. This counter electrome- 'tive force willsend a current through the c'1rcu1t6,-7.- This refers to the --aud1ofre-' quency wave, since the telephone coil will act as choke towardsradio frequency current. The detector 7 will rectify, the current thusmaking the system operative.

My invention is embodied in the circuit diagrammatically illustrated inFig. 3. In this figure, an antenna A is connected to ground through theprimary 1 of an oscillation transformer.v The secondary 3 of thetransformer is shunted by a variable condenser 4 to, form a tunablecircuit generally indicated by I. One side of tuned circuit I isgrounded, and the other side is connected to one end of a coil or openconductor 6 whichis provided with a shunt condenser 7. Coil 6 is ininductive relation to another coil 8 which, I with variable condenser 9,forms a second tuned circuit 11. One side of circuit This grounded,preferably the side adjacent the end of coil 6 which is conneceted tocircuit 1, and the other side of circuit 11 is connected to grid 11 of avacuum tube 10. V The vacuum tube may serve asa repeater, an ampllfieror a detector, as desired. The plate 12 of the tube 'is connected I tothe battery 14 and the filament 13 through the primary winding 15 of atransformer, the secondary 16 being connected to the output circuit.-The transformer may or may not be provided with an iron core asdesired. Coil 8 is arranged in non-inductive relation to c0113. I

r The arrangement shown inFig. 3 is some what similar to. that shown inFig. 1, but the operation of Fig. 3 has to do only with the effectrofthe radio frequency currents; The

The incoming signal sets .up a circulating current through the coil?)and the variable condenser 4. The currentpressure will be propagatedthrough the leads to the c'oil 6 and condenser 7, The first transientwave 7 impulse will force the electrons through the denser, butthe-reaction; of the coil to suchwindings of the coil and. against thecom a wave is different from thatof the condenser. Thecoil will act likean elastic wall,"

and will react upon the current impulse, the action and reaction beingequal and opposite. The transient current magnet1zes the core and theflux sets up acounter-eleo' tromotive force. When again the electroncurrent strikes the condenser, these electrons will be first stored, asin a reservoir, then discharged during the vnext half cycle.

Consequently the counter-electromotive force set up in the coil 6 willsendv a current The current in thelead 5 will be small, the

pressure of the current in the circuit 3, 4

being opposed by the pressure of the current in the circuit 6,77.Current flowing in coil 6 induces current in coil 8 and excites tunedcircuit II. Potentialvariations acros'stuned circuit II areimpressedupon grid 11' to operate vacuum tube 10. l

' While I have'shown an external condenser '7 connected'in shunt to,coil- 6, it is to be understood that the coil may be so designed thatits natural distributed capacity will serve the function of condenser 7,and an additionalicapacity need not be employed.

7 11V do not intend to be limited to any particular quantities'ordimensionsof the variious elements of my invention, but for the.purpose-of illustration only, I find through the condenser 7, thiscurrent being 7 in step with the current in the circuit 3,4;

that fora tuning range; from 200 -to 550 meters satisfactory results areobtained when coil 6 is 2 inches in diameter and has approximately 42turns, while coil 8 it 2% inchesin diameterand has approxi- The seriesof tuned circuits connected in cascade may be termed a .filter, and inmy invention each tuned circuit is connected with the succeeding onebymeans of unilateral, aperiodic coils or circuits. It is; ;possible toobtain voltage amplification of the waves within. the filter itselfg-The ratio of thevolta'ge across'coil 8 to the voltage across coil 3maybe eitherajstep-up or a step-down ratio; depending upon theefliciency of energy transfer through the filter. Of course, this stepup .in voltagedoes not mean increased energy, since there is no energyamplification Wltl'llil the filter itself.

* v The mannerof transfer of energy through the filter -may beexplainedwith the'aidof the vector diagramshownin Fig.2. J representsthej;current-circulating in circuit I.

If the current were free to flow through the lead 5', coil 6 and someway back again without reducing the amount of current cirdenoted by F(Fig. 2) will have the same phase. Following the'common way ofdrawingvecto-r diagrams the electromotive force E 'set up in thesecondary winding 8 will lag 90 degrees behind the flux. The condenser 9being tuned to resonance, the secondary load current J flowing throughit will lead the voltage by nearly 90 degrees. It'will be opposed by theload component J of: the current in the primary winding 6,v andconsequently this load component will be nearly 180 degrees out of phasewith the flux, and nearly opposed to magnetizing currentJ The vector sum,of both-the actual current J 7 through the condenser 7-will thus besmall compared with both of them, the magnetizing current and the loadcurrent. A comparatively small current in the aperiodic coil 6 (Fig. 3)will cause alarg'e circulating current in the circuit II. The terminalvoltage V across coil 8 will be greater, equal to or smaller than theterminal voltage across coil 3, depending upon the nature of the coil 6and condenser 7 This coil and condenser should be. preferably sodesigned that astep-up voltage ratio exists. 7

Thecomparative efficiency of this energy transfer can be seen from thevector diagram. The energy transferred from e011 6 to the circuit 8,9will be proportional to the current vector J the energy lost in coil 6will again be proportional to the vector J Thus only a small portionofenergy is lost.

Another way to explain this filter circuit would be 'to consider theunilateral coil as a diminutive transmitting aerial with a very smallnatural capacity, but a great se lf-inductance. 'This diminutiveaerialis inductively coupled to the next filter stage acting as receiver.vNotwithstanding the small size of the unilateral coil, compared with anaerial, the former may be very efiicient. The natural capacity may besmaller, but it has afar greater self-inductance. In an aerial the'energy will be stored mainly in the conductor itself and in theelectrical field surrounding it, in the unilateral coil direct inductiveor capacitative coupling. Take for example, theordinary transformer typeof coupling in which two tuned circuits are inductively coupled.Considering each circuit alone, the voltage and current are at a miximumwhen the circuit is tuned to resonance, but when the two are coupledtogether the resonance curve generally shows two peaks, which broadenthe curve and destroy selectivity. In order to eliminate the double-humpin the curve the coupling must be reduced. This so-called optimumcoupling, however, is very loose, and does not permit efficient transferof energy. I

In my systemthere is'no such harmful reaction between the tunedcircuits. The amplification curve for each circuit shows a single peak,the resonance peak of the second circuit being sharper than that of thefirst. If a number of filter stages are contive than the preceding one.If all circuits are tuned simultaneously, the last circuit will have thegreatest effect upon the selectivity, and with the number of stages theselectivity will rise notin geometric progression, but in a progressionsteeper than the geometric. The energy transfer will be greatest for thefrequencies near the resonance, whereas for frequencies farther awaythis transfer is very small. It may be said that a part of the peakenergy has been transferred to the next circuit. There is no tendency tobuild up a double peak.

The arrangement shown in Fi 4 is an extension of the circuit shown in 1*ig. 3, and like elements are represented by the same reference numerals.In this arrangement there are five tuned circuits I-V in the entire 1filter, but an amplifying tube 10 is inserted between circuit II andcircuit III for the purpose pling instead of the inductive couplingshown. In order to reduce the effect of natural capacity between coil 6and coil 8, it will be advantageous to place coil 6 at the grounded endof coil 8. This applies also to coils 15,118 and 21. If there beconsiderable capacity between coils 6 and 8, this capacity will providea return path to circuit ofy Elli

V J to Fig. 4.

v i In the is impressed upon a second amplifying tube It is to be notedthat the functionfof the tubes'is to supply additional energy to thewaves to compensate for the loss:in the filter and to amplify thevoltage. The tubes are not relied upon to prevent reaction between thecircuits, and thenumber of tubes inserted in the filter-is kept as smallas possible consistent with the amplification required, I

' In'Fig. 5 I provide additional amplifica tion by connecting anamplifying tube in cascadewith tube 10 through'an untuned transformer28-29. This transformer may or may not be provided with an iron core, as

desired-. Fig. 5 .is similar in 'otherrespects preferred form of :myinvention, shown in Fig. 6, I first amplifythe incoming signal beforeentering the filter by amplifying tube 40, the. grid ofw'hichisconnected directly to the antenna," and to ground through a choke coil31. The choke coil is preferably so designed as to render the an tennacircuit aperiodic. The filter in this arrangement consists of anunbroken cascade of resonant circuits I to 'IV', or as many" as desired.After passing through the filter the waves are impressed upon an untuned1 The last amplifier tube is coupled by transformer 61, 62 to a detectortubex70, which voltage amplifier consisting of vacuum tubes and 60,coupled by a transformer 51,52.

detectsrthe' high frequency wave and derives therefrom the low frequencysignal. If'desired,'the low frequency signal current'may be. amplifiedby an audio'freque'ncy amplifier indicated at T. V The advantage of thearrangement shown inIFig 6 is that by first amplifying the in; comingsignal Wave before it reaches the filter a longer and more selectivefilter maybe used before the voltage: amplification stage.

The first amplifying tube 40 will; of course, also amplify the voltage.In this 'position a special tube giving great energyiamplifiization maybe employed.

' In Fig. v6 the amplifying "tube is coupled to the first filter-circuitI by means of a unilateral coil 46. A choke coil 33 has been added toconnect the plate with *the'bat tery 42. This Way of coupling shows .agreater selectivity than that of Fig. 6, a unilateral coupling is moreselective than the transformer coupling. I

WhileI have offered certain theories of operation in the foregoingdescription of my invention, it is to be understood that the scope of-myinvention is not-to be restricted prising a number of tuning-stagesconnected in cascade, means for'indu'ctively coupling "these stages withsubstantial elimination of mutual impedances between adjacent stages,said means including an open coil, and means of amplification associatedwith these stages. 2." An electric signaling system comprising a numberof tuning s'tages connected in cascade, means for couplingsaidstag'es,fineluding a substantially open coil in conduc tive relation toa stage and inductively coupled to the following stage, said coil havinga substantial distributed capacity, and means of amplificationassociated with the stages.

3. An electric wave filter comprising a number 'of tuningstagesconnected in cascade and means for coupling s'aidj stages, thesemeans including a substantially open coil in conductive relation to a'stagc and inductively coupled to the following stage and having anegligible coupling capacity. 4:."An electric wave filter comprising anumber of stages connected in cascade, each stage consisting of a'coilshunted by'a condenser, said coil and condenser forminga circuitresonant; tothe desired frequency,

and means for coupling said stages, these means including asubstantially open coil in conductive'relation to a resonant stage andinductively coupled with the coil of the cuit andinductively coupled tothefollowing circuit, said coil having a substantial distributedcapacity, the corresponding parts in each'circuit having no commonmagnetic field. v I

'6. An electric wave filter comprising a number of stages connectedin'ca'scade, each stage including a circuit resonant to the desiredfrequency, and means for coupling two consecutive "circuits includingasubstan tially open coil connected with one and inductively coupledwith the other circuit, the

corresponding parts of each circuit having 7 substantially no commonmagnetic or electric field.

7. A system for selecting electric Waves comprising a pair of circuitsresonant to the frequency to be selected and an open coil innon-inductive conductive relation With one of the circuits andinductively coupled to the other circuit said coil having a substantialdistributed capacity. 8. A system for selecting electric wavescomprising a series of independent tuned circuits arranged in cascade,and means for coupling said circuits comprising an open coil external toboth circuits and connected to the preceding circuit and inductivelycoupled to the following circuit, said coil having a shunted capacity.

9. A system for selecting electric Waves comprising a series ofindependent tuned circuits arranged in cascade, each circuit comprisingan inductance coil shunted by a condenser, each coil inductively coupledto an open coil having one end connected to the preceding circuit.

10. An electric signal selecting system comprising tWo resonant circuitsconnected in'cascade each of the circuits consisting of an inductanceshunted by a capacity, the

I inductances being in non-inductive relation to each other, thecircuits having one common point, and an open coil having one end freeand its other end connected to a point of the preceding circuitdiffering from the common point, said coil being inductively coupled tothe coil in the succeeding circuit.

11. An electric signaling system comprising an aerial, a selector, andan amplifier, said selector forming a continuous unit comprising anumber of tuning stages connected in cascade, and means forsubstantially eliminating resonance distortive reaction of a stage uponthe preceding stage, said means including an open coil.

12. An electric Wave receiving system comprising an antenna, a selectorconsisting of a number of stages in cascade, each stage including acircuit resonant to the desired frequency, and of means including anopen coil for coupling said stages With substantial elimination ofresonant distortive reaction therebetWeen, and means for preventingvariations in the antenna constants from afi'ecting the tuningadjustments of said selector, said last mentioned means comprising anelectron discharge device coupling the selector to the antenna.

GEORGE A. SOMERSALO.

